CN - Chapter 2 - Neurons and Glia Flashcards
glial cell
A support cell in the nervous system. Glia are classified into four categories:
- astrocytes
- oligodendroglia
- Schwann cells
- microglia
Astrocytes regulate the extracellular environment of the brain, oligodendroglia and Schwann cells provide myelin, and microglia scavenge debris.
neuron
The information processing cell of the nervous system; also called a nerve cell. Most neurons use action potentials to send signals over a distance, and all neurons communicate with one another using synaptic transmission.
histology
The microscopic study of the structure of tissues.
Nissl stain
A class of basic dyes that stain the somata of neurons;
named for its disoverer, German histologist Franz Nissl (1860-1919).
cytoarchitecture
The arrangement of neuronal cell bodies in various parts of the brain.
Golgi stain
A method of staining brain tissue that shows neurons and all of their neurites;
named for its disoverer, Italian histologist Camillo Golgi (1843-1926).
cell body / soma / perikaryon
The central region of the neuron containing the nucleus.
neurite
A thin tube extending from a neuronal cell body;
the two types are axons and dendrites.
axon
A neurite specialized to conduct nerve impulses, or action potentials, normally away from the soma.
dendrite
A neurite specialized to receive snyaptic inputs from other neurons.
neuron doctrine
The concept that the neuron is the elementrary functional unit of the brain and that neurons communicate with each other by contact, not continuity.
cytosol
The watery fluid inside a cell.
organelle
A membrane-enclosed structure inside a cell;
examples are the nucleus, mitochondrion, endoplasmic reticulum, and Gogi apparatus.
cytoplasm
Cellular material contained by the cell membrane, including the organelles but excluding the nucleus.
nucleus
- The roughly spherical organelle in a cell body containing the chromosomes.
- A clearly distinguishable mass of neurons, usually deep in the brain.
chromosome
A structure in the cell nucleus containing a single linear thread of DNA.
DNA (deoxyribonucleic acid)
A double-stranded molecule constructed from four nucleic acids that contains the genetic instructions for a cell.
gene
A unit of heredity;
a sequence of DNA that encodes a single polypeptide or protein.
gene expression
The process of transcribing the information from a gene into messenger RNA (mRNA);
a gene is a segment of DNA carrying the instructions for a single protein (or polypeptide).
protein
A polymer of amino acids strung together by peptide bonds.
protein synthesis
The assembly of protein molecules in the cell’s cytoplasm according to genetic instructions.
mRNA (messenger ribonucleic acid)
A molecule constructed from four nucleic acids that carries the genetic instructions for the assembly of a protein from the nucleus to the cytoplasm.
transcription
The process of synthesizing a messenger RNA molecule according to genetic instructions encoded in DNA.
promoter
A region of DNA that binds RNA polymerase to initiate gene transcription.
transcription factor
A protein that regulates the binding of RNA polymerase to a gene promoter.
RNA splicing
The process by which introns, the regions of a primary RNA transcript that are not used to code protein, are removed.
amino acid
A chemical building block of protein molecules, containing a central carbon atom, an amino group, a carboxyl group, and a variable R group.
translation
The process of synthesizing a protein molecule according to genetic instructions carried by a messenger RNA molecule.
ribosome
A cellular organelle that assembles new proteins from amino acids according to the instructions carred by messenger RNA.
rough endoplasmic reticulum (rough ER)
A membrane-enclosed cellular organelle with robosomes attached to its outer surface;
a site of synthesis for proteins destined to be inserted into membrane or to be enclosed by membrane.
polyribosome
A collection of several ribosomes floating freely in the cytoplasm.
smooth endoplasmic reticulum (smooth ER)
A membrane-enclosed organelle that is heterogeneous and performs different functions in different locations.
Golgi apparatus
An organelle that sorts aand chemically modifies proteins that are destined for delivery to different parts of the cell.
mitochondrion
An organelle responsible for cellular respiration.
Mitochondria generate adenosine triphosphate (ATP) using the energy produced by the oxidation of food.
ATP (adenosine triphosphate)
The molecule that is the cell’s energy source. The hydrolysis of ATP to produce adenosine diphosphate (ADP) releases energy that fuels most of the biochemical reactions of the neuron. ADP is converted back to ATP in the mitochondria.
neuronal membrane
The barrier, about 5 nm thick, that separates the inside of a nerve cell from the outside;
consists of a phospholipid bilayer with proteins embedded in it;
encloses the intracellular organelles and vesicles.
cytoskeleton
The internal scaffolding that gives a cell its characteristic shape;
consists of microtubules, neurofilaments, and microfilaments.
microtubule
A polymer of the protein tubulin, forming a straight, hollow tube 20 nm in diameter.
Microtubules, a component of the cytoskeleton, play an important role in axoplasmic transport.
microfilament
A polymer of the protein actin, forming a braided strand 5 nm in diameter;
a component of the cytoskeleton.
neurofilament
A type of intermediate filament found only in neurons, 10 nm in diameter;
an important component of the neuronal cytoskeleton.
axon hillock
A swelling of the axon where it joins the soma.
axon collateral
A branch of an axon.
axon terminal
The end region of an axon, usually a site of synaptic contact with another cell;
also called terminal bouton or presynaptic terminal.
terminal bouton
The end region of an axon;
usually a site of synaptic contact with another cell;
also called an axon terminal.
synapse
The region of contact where a neuron transfers information to another cell.
terminal arbor
Branches at the end of an axon terminating in the same region of the nervous system.
innervation
The provision of a synaptic input to a cell or collection of cells.
synaptic vesicle
A membrane-enclosed structure, about 50 nm in diameter, containing a neurotransmitter and found at a site of synaptic contact.
synaptic cleft
The region separating the presynaptic and post synaptic membranes of neurons.
synaptic transmission
The process of transferring information from one cell to another at a synapse.
neurotransmitter
A chemical released by a presynaptic element upon stimulation that activates postsynaptic receptors.
axoplasmic transport
The process of transporting materials down an axon.
anterograde transport
Axoplasmic transport from a neuron’s soma to the axon terminal.
retrograde transport
Axoplasmic transport from an axon terminal to the soma.
dendritic tree
All the dendrites of a single neuron.
receptor
- A specialized protein that detects chemical signals, such as neurotransmitters, and initiates a cellular response.
- A specialized cell that detects environmental stimuli and generates neural responses.
dendritic spine
A small sac of membrane that protrudes from the dendrites of some cells and recieves synaptic input.
unipolar neuron
A neuron with a single neurite.
bipolar neuron
A neuron with two neurites.
multipolar neuron
A neuron with three or more neurites.
stellate cell
A neuron characterized by a radial, star-like distribution of dendrites.
pyramidal cell
A neuron characterized by a pyramid-shaped cell body and elongated dendritic tree;
found in the cerebral cortex.
spiny neuron
A neuron with dendritic spines.
aspinous neuron
A neuron lacking dendritic spines.
primary sensory neuron
A neuron specialized to detect environmental signals at the body’s sensory surfaces.
motor neuron
A neuron that synapses on a muscle cell and causes muscle contraction.
interneuron
Any neuron that is not a sensory or motor neuron;
also describes a CNS neuron whose axon does not leave the structure in which it resides.
astrocyte
A glial cell in the brain that supports neurons and regulates the extracellular ionic and chemical environment.
oligodendroglial cell
A glial cell that provies myelin in the central nervous system.
Schwann cell
A glial cell that provides myelin in the peripheral nervous system.
myelin
A membranous wrapping, or sheath, around axons, provided by oligodendroglia in the CNS and Schwann cells in the peripheral nervous system.
node of Ranvier
A space between two consecutive myelin sheaths where an axon comes in contact with the extracellular fluid.
ependymal cell
A type of glial cell that provides the lining of the brain’s ventricular system.
microglial cell
A type of cell that functions as a phagocyte in the nervous system to remove debris left by dead or dying neurons and glia.
What are two factors that distinguish the axon from the soma?
- No rough ER extends into the axon, and there are few, if any, free ribosomes.
- The protein composition of the axon membrane is fundamentally different from that of the soma membrane.
How does the cytoplasm of the axon terminal differ from that of the axon?
- Microtubules do not extend into the terminal.
- The terminal contains numerous small bubbles of membrane, called synaptic vessicles, that measure about 50 nm in diameter.
- The inside surface of the membrane that faces the synapse has a particularly dense covering of proteins.
- It has numerous mitochondria, indicating a high energy demand.
State the neuron doctrine in a single sentence. To whom is this insight credited?
The neuron doctrine is the idea that the neurons are not continuous with one another but are discrete cells that communicate by contact and not by continuity.
This insight is credited to Santiago Ramón y Cajal.
Which parts of a neuron are shown by a Golgi stain that are not shown by a Nissl stain?
The Golgi stain shows the neuronal cell body with the dendrites and the axon. The Nissl stain shows only the cell body.
What are the three physical characteristics that distinguish axons from dendrites?
The three physical characteristics that distinguish axons from dendrites are:
i) The cell body usually gives rise to a single axon while many dendrites extend from the cell body.
ii) The axon is of uniform diameter throughout its length while dendrites rarely extend more than 2 mm in length.
iii) The branches of an axon generally extend at right angles while dendrites generally taper to a fine point.
Among the following structures, state those which are unique to neurons and the ones that are not: nucleus, mitochondria, rough ER, synaptic vesicle, and Golgi apparatus.
The synaptic vesicle is unique to neurons whereas the nucleus, the mitochondria, the rough ER, and Golgi apparatus are not unique to neurons.
What are the steps by which the information in the DNA of the nucleus directs the synthesis of a membrane-associated protein molecule?
Protein synthesis occurs in the cytoplasm; DNA never leaves the nucleus. To transport the information necessary for protein synthesis, mRNA is used…
The process of assembling a piece of mRNA that contains the information of a gene is called transcription and the resulting mRNA is called the transcript…
Amino acids are brought to the ribosome by transfer RNA (tRNA). The assembling of proteins from amino acids under the direction of the mRNA is called translation.
Colchicine is a drug that causes microtubules to break apart or depolymerize.
What effect would this drug have on anterograde transport?
What would happen in the axon terminal?
Vesicles containing molecules needed at the axon terminal “walk down” the microtubules within the axon on “legs” provided by a protein called kinesin. The
process is fueled by ATP. Kinesin moves material only from the soma to the terminal. Movement in this direction is called anterograde transport.
The application of colchicines causes microtubules to disintegrate, and when applied to the axon disrupts
the path for anterograde transport. As a result, all movement of material from the soma to the terminal (anterograde transport) ceases. If the colchicines application does not kill the whole cell, then the material to be transported will accumulate on the side of the axon closest to the soma.
Classify the cortical pyramidal cell based on (a) the number of neurites, (b) the presence or absence of dendritic spines, (c) connections, and (d) axon length.
Classification of the cortical pyramidal cell is as follows:
(a) Cortical pyramidal cells have three or more neurites and are multipolar.
(b) Cortical pyramidal cells have dendritic spines.
(c) Axons of cortical pyramidal cells project to other cortical areas and also to several subcortical areas as well.
(d) In the cerebral cortex, pyramidal cells usually have long axons that extend to other parts of the brain and are therefore Golgi type I neurons.
What is myelin and what does it do? Which cells provide myelin to the central nervous system?
Myelin refers to layers of glial membrane that insulate axons. Myelin speeds the propagation of nerve impulses down the axon. The oligodendroglial cells provide
myelin in the central nervous system.
(Schwann cells provide myelin in the peripheral nervous system.)
